The purpose of a catalytic converter is to convert pollutant materials in engine or turbine exhaust gas streams, e.g., carbon monoxide, unburned hydrocarbons, nitrogen oxides, etc., to carbon dioxide, nitrogen and water. Conventional catalytic converters utilize a ceramic honeycomb monolith having square, circular, or triangular straight-through openings or cells with a catalyst or catalysts deposited on the walls of the cells, catalyst coated refractory metal oxide beads, e.g., alumina beads, or a corrugated thin metal foil monolith, e.g., ferritic stainless steel foil, having catalyst material carried on or supported by the surface. The catalyst is normally a noble metal, e.g., platinum, palladium, rhodium, ruthenium, or a mixture of two or more of such metals. The catalyst catalyzes a chemical reaction, mainly oxidation, whereby the pollutant is converted to a harmless by-product which then passes through the exhaust system to the atmosphere.
However, conversion is not efficient initially when the exhaust gases and the catalyst are each relatively cold. To be effective, the catalyst and the surface of the converter with which the gases come in contact must be at a minimum temperature, e.g., 390 F. for carbon monoxide, 570 F. for volatile organic compounds (VOC) and 1000 F. for methane or natural gas. Otherwise, conversion to harmless byproducts is poor and cold start pollution of the atmosphere is high. Once the exhaust system has come to its operating temperature, the catalytic converter is optimally effective. Hence, it is necessary to contact relatively cold exhaust gases with hot catalyst in order to effect satisfactory conversion at engine start-up. Both compression ignited (diesel) and spark ignited internal combustion engines have this need.
To accomplish this pre-ignition heat up, electrically heatable catalytic converters have been developed. These are connected to the engine voltage source, e.g., at 12 volt to 60 volt battery-alternator power supply system. Reference may be had to copending commonly owned application Ser. No. 587,219 filed Sep. 24, 1990 in the names of William A. Whittenberger and Richard C. Cornelison for disclosure of a suitable electrically heatable catalytic converter and power means for heating it. Thee power means are useful in the present invention to provide the requisite power for rapid and repeatable heating to an optimum light-off temperature (650 F. to 750 F.) of the electrically heatable catalytic converter in a minimum amount of time, e.g., 2 to 30 seconds. The electrically heatable catalytic converter (EHC) effectively jump starts the temperature in the exhaust in order to trigger the light-off of the pollutants and utilize latent chemical energy. Reference may also be had to the patents to Kitzner, U.S. Pat. Nos. 3,768,982 and 3,770,389 each dated Oct. 30, 1973 which disclose electrically heated catalytic converters.
Reference may also be had to International PCT publication numbers WO 89/10470 and 10471 filed Nov. 2, 1989. These disclose electrically heatable catalytic converters useful in automobiles.
Reference may also be had to U.S. Pat. No. 4,711,009 dated Dec. 8, 1987 and issued to Cornelison et al which provides details for the preparation of polycellular corrugated thin metal (ferritic stainless steel) monoliths having a catalyst deposited on the surface, which process may be used in the fabrication of the present devices.
The present invention solves a problem which exists in after market vehicles, for example, and which, for the most part, are equipped with ceramic core catalytic converters as mentioned above. With the ever tightening rules by states, e.g., Calif., there is a great need for a simple device for retrofitting such automobiles with an electrically heatable catalytic converter in the same exhaust line already containing a conventional ceramic core catalytic converter. Such device must be dimensioned and configured to fit within the standard exhaust lines, for example, those used on passenger automobiles. These have a diameter on the average of 2.5". Flanges for such exhaust pipes are currently available, and the devices hereof should be clampable between such flanges fitted over the severed ends of the exhaust pipe. For Diesel engines, a larger diameter, up to 6 inches or more, may be used. Thus, by cutting the exhaust pipe, ahead of or after the conventional catalytic converter, attaching, e.g., by welding, standard exhaust pipe flanges, and inserting a device of the present invention, current automobiles may be retrofitted with an electrically heatable catalytic converter to enable reduction in the production of pollutant materials at, for example, start-up. Alternatively, these devices may be attached to the engine directly in the exhaust conduit leading from the cylinder to the manifold, one for each cylinder. Depending on size and space constraints, these devices may be from about 2" to about 8" long. Thus, these devices can be used for retrofitting current vehicles. They can also be used to replace worn out devices. More over, because of their easy replaceability, the devices can be made intentionally smaller and less expensive, and designed for periodic replacement as needed.